Seized Ali Seatpost / Steel Frame

The alu seat lost has corroded. Aluminium oxide is bigger than the original aluminium. Aluminium oxide is also pretty stable (think of Anodising). That’s why oil isn’t going to work. Bottom bracket out, invert the frame over a steel bowl or bucket and pour in a sodium hydroxide solution. Gloves and goggles a must.

Remove the saddle and give the top of the seatpost saddle rail clamp a sharp whack or two from a hammer, this may break the galvanic corrosion and then try the clamp in a vice trick – don’t worry, i’ve never failed to remove stuck seatposts, even from 40+ year old steel framed road bikes.

It takes time, patience, various noxious/corrosive chemicals and knowledge of just how far you can push materials along with a big hammer and a handful of expletives thrown in for good measure.

I’d normally just leave it but I need to get my bike into a cardboard box and onto a flight in two weeks time. It ain’t gonna fit in any box if I can’t get the seat post out.

Tried the 1st couple of suggestions on Sheldon Brown… Lever the seat tube ‘ears’. Clamp the seatpost in a vice and turn the frame. The frame was flexing and the tube not budging. I didn’t want to push it any further.

I’ve sprayed a bit of GT85 into the seat tube from the bottle bosses and left the bike upside down but Sheldon suggests oil won’t work. Suggests Ammonia based solution so I’ve ordered some ammonia cleaner.

Anyone had any joy with the Ammonia technique? Or Cola? Not stressed yet but I soon will be as the date of my flight gets nearer.

You don’t want to tap it with a saddle fitted as that will dampen the percussive jolt, you shouldn’t need to hit it that hard anyway – just a few sequential taps should get it shocked enough to free off the galvanic bond.

Using a blow torch heat the seatpost focussing the heat about 50-80mm above the frame – get it as hot as you dare without the paint on the frame bubbling. Better if you point the flame upwards slightly towards the saddle clamp end and the heating of the seatpost in the frame is entirely conductive. You can get a lot more heat in there without damaging the paint than you would imagine.

Turn off blow torch and invert frame plunging the seatpost into a bucket of water. Will make ace rushing noise and steam will rush out of the BB.

Repeat 8 or 9 times at least.

Then put seatpost clamp in vice and twist frame – if like mine it’ll make some god awful creaking/cracking noises as it releases.

I removed a seatpost from a frame by drilling a hole through seatpost, sliding an old long screwdriver through it, laying bike side down and tapping it with a hammer, (and then applying a bit more force with my foot!) Was careful and it worked, unable to loosen seat post with vice or with seat left on. New seat post now required.

I would try convert‘s suggestion except I’d wrap the seat tube in an old towel and keep it wet while I was heating the post. The aim should be to expand the post but not the tube so that the corrosion layer is crushed. Rather than dunk the post in cold water, I’d let it cool naturally and once it’s below boiling temperature I’d drip Plusgas or similar onto the joint so that it’s drawn in as it cools. Not done it on a seat post but I’ve had success with this method on steel bleed valve in an alloy brake caliper (for a car).

I’ve just used the last resort on my seatpost. Allu seatpost, Allu shim, Titanium frame. Cut the seatpost off approx. 2 inches above the frame and used a hacksaw blade to cut inside the tube all the way down. As soon as it was cut all of the way down I clonked it gently with a hammer just to get it moving and used pipe grips to get it out. Certainly not a pretty way of doing it but pretty much guaranteed to get it out.

A local bike frame builder applied his torch to my steel frame and partially melted the alloy post enabling him to get it out . The seat tube needed reaming and repainting but was fine afterwards and is still in daily use by my son at uni. Oh, it needed a new seatpost!
My next challenge is to extract my alloy post from my carbon road bike. The seat is at the right height which is why it has taken months for me to get on with it but now I need to shrink bike for travel.

Spent the last week overnight soaking in various solutions, coke, Ammonia etc. Riding the bike all week with the clamp not done up in the hope it might work loose. No chance.

Final attempt to get the tube to budge using a vice just rotated the saddle clamp in the seattube. Resorted to Stillsons on the post which just crushed it.

Spent Sat AM hacksawing away. Managed to get 4 cuts into the post lengthways but trying to ‘fold’ the seatpost just proved the tube was still stuck solid somewhere below where the top tube and seat stays joins the seat tube.

Had to resort to the Caustic Soda method.

Preparation is the key here. Completely stripped the frame. Sawed the post flush to the frame. I turned the frame upside down and bunged up the hole with big dollop of blue tac and then wrapped a plastic bag taped tightly.

I used a syringe to squirt the solution into the bottle cage mounts and then plugged the mounts up with more blu tac and plastic bag / tape.

I made a fearsomely strong solution, probably 50/50 volume approx. Water in a plastic jug poured in caustic soda then mixed with a wooden spoon. It gets warm. By now PVC gloves and full goggles are on.

Solution injected and sealed then I left for 1/2 hour until the bubbling stopped and cooled down. Some really nasty black stuff occasionally bubbled right ‘up’ the seattube and out of the hole in the bb shell. I just rinsed this stuff away when it happened. After 1/2 hour I inverted and poured the black stuff into a plastic bucket. Rinsed the tube and repeated.

The reaction is more fearsome with freshly made solution. Not sure why the solution would go off in 30 mins, or whether the reaction was better whilst the solution was warm.

I probably repeated this twice last night, then left it overnight with some older solution overnight reacting less violently, then twice this morning. The whole tube had disappeared. There’s a little paint loss around the top of the seat tube. But considering the chemical attack…